1. Field of the Invention
The present invention generally relates to the storage and transfer of wafers typically used in the fabrication of integrated circuits. Specifically, the invention relates to the end effector, or blade, of a wafer handler used to transfer wafers through and between chambers in a system, for processing the wafers.
2. Background of the Related Art
Vacuum processing systems for processing 100 mm, 200 mm, 300 mm or other diameter wafers are generally known. Typically, such vacuum processing systems have a centralized transfer chamber mounted on a monolith platform. The transfer chamber is the center of activity for the movement of wafers being processed in the system. One or more process chambers mount on the transfer chamber at slit valves through which wafers are passed by a wafer handler, or robot, in the transfer chamber. The valves close in order to isolate the process chambers while wafers are being processed therein. The wafer handler transfers the wafers through the transfer chamber and between the various other chambers attached to the transfer chamber.
Some common transfer chambers have facets to accommodate four to six chambers. The process chambers include rapid thermal processing (RTP) chambers, physical vapor deposition (PVD) chambers, chemical vapor deposition (CVD) chambers, etch chambers, etc. Physically, the process chambers are either supported by the transfer chamber and its platform or are supported on their own platform. Inside the system, the transfer chamber is typically held at a constant vacuum; whereas, the process chambers may be pumped to a greater vacuum for performing their respective processes. Afterward, the chamber pressure must be returned to the level in the transfer chamber before opening the valve to permit access between the chambers.
For some vacuum processing systems, such as the Centura (trademark) system from Applied Materials, Inc., access to the transfer chamber for wafers from the exterior of the system, or from the manufacturing facility, is typically through one or more load lock chambers. For some other vacuum processing systems, such as the Endura (trademark) system from Applied Materials, Inc., a series of other chambers, including a buffer chamber, are provided between the transfer chamber and the load lock chambers. Thus, the transferring of the wafers through the vacuum in the system proceeds in stages, with the buffer chamber typically operating at about 1xc3x9710xe2x88x926 torr, the transfer chamber typically operating at about 1xc3x9710xe2x88x927 torr and the process chambers typically operating at about 1xc3x9710xe2x88x929 torr in the case of physical vapor deposition process chambers.
The buffer chamber is an intermediate transfer chamber that may have optional preprocessing or post-processing chambers attached to it for performing additional processing steps on the wafers. Additionally, a pre-clean chamber and a cool-down chamber are interposed between the buffer chamber and the transfer chamber. Since the buffer chamber and the transfer chamber are typically held at different vacuum levels, the pre-clean chamber transitions the wafers from the vacuum level of the buffer chamber to the vacuum level of the transfer chamber in addition to cleaning the wafers in preparation for processing in the process chambers. After undergoing the primary process, the cool-down chambers transition the wafers from the vacuum level of the transfer chamber to the vacuum level of tie buffer chamber while cooling the wafers. Another wafer handler, similar to the one disposed in the transfer chamber, is disposed within the buffer chamber in order to transfer the wafers through the buffer chamber and between the various chambers attached thereto.
The load lock chambers cycle between the pressure level of the ambient environment and the pressure level in either the transfer chamber or the buffer chamber in order for the wafers to be passed therebetween, so the-load lock chambers transition the wafers between the atmosphere pressure of a very clean environment to the vacuum of the system. The load lock chambers attach to a mini-environment which transfers wafers in a very clean environment at atmospheric pressure from wafer pods to the load lock chambers. Thus, the mini-environment has another wafer handler for transferring the wafers.
The wafer handlers in the transfer chamber and the buffer chamber are typically very similar, if not identical. An example of such a wafer handler 10 is shown in FIGS. 1a and 1b. the wafer handler 10 is capable of rotational movement, but not translational movement since it is fixed in the center of its chamber. The wafer handler 10 has an end effector 12, 14, or blade, attached to an arm assembly 16 attached to the rotating portion 18 of the wafer handler 10. A wafer sits on the end effector 12, 14 in order to be transferred. A sensor beam may be projected through the wafer sense hole 15 in order to sense the presence of a wafer on the end effector 12, 14. The sensor beam may be an infrared beam directed at a detector. The wafer sense hole 15 is typically a standard size, and may be about 0.87 inches, or 22 mm, in radius. The arm assembly 16 moves the end effector 12, 14 radially outward from and inward towards the wafer handler 10 in order to insert a wafer into or retrieve a wafer from a chamber.
The wafer handler in the mini-environment is typically different from those in the transfer chamber or the buffer chamber, since it is usually capable of translational movement as well as rotational movement. A top view of an example of such a wafer handler 20 is shown in FIG. 1c. The wafer handler 20 is typically track mounted so that it can move back and forth inside the mini-environment in order to service each of the pod loaders and load lock chambers attached thereto. The wafer handler 20 has an end effector 22 attached to an arm assembly 24 attached to the rotating portion 26 of the wafer handler 20. A wafer sits on the end effector 22 in order to be transferred. The arm assembly 24 moves the end effector 22 radially outward from and inward towards the rotating portion 26. The contact portion 25 of the end effector 22 is typically the only part of the end effector 22 that contacts the wafer. The contact portion 25 typically uses vacuum suction to hold the wafer. Vacuum suction Is not a practical method to hold a wafer inside the transfer chamber or the buffer chamber, however, since these areas are already subject to a vacuum, which would lessen the hold of the vacuum suction. Additionally, it is desirable to have only one style of end effector, which may be used with all wafer handlers, in order to reduce the number of parts used in a processing system.
The end effector 14, shown in FIG. 1a, has a constant width from the end effector mounting 27, or robot blade wrist, to the free end. A short recess in the free end forms two projections at the free end. A wafer is supported on small shelves located near the free end on the two projections and near the end fixed at the mounting 27. The shelf supports may provide no more than about 120 mils of space between the wafer and the end effector 14. For 300 mm wafers, the width poses a problem with the exclusion zones defined by the SEMI 300 mm Wafer Carrier and Interface Standard, a standard set by Semiconductor Equipment and Materials International to create, inter alia, an industry standard configuration for a wafer carrier.
The exclusion zones are areas within a 300 mm wafer carrier or holder reserved for the wafer carrier to support the wafer and are illustrated by the areas 100, 102 as shown in FIG. 4. The exclusion zones 100 are about 29 mm wide, 170 mm long and 250 mm apart. The exclusion zones 102 are about 25 mm wide, 32 mm long and 100 mm apart. The center of a wafer will be almost directly in the geometric center of the combined exclusion zones 100, and offset from the exclusion zones 102 by about 120 mm. An end effector may not cross these areas while lifting a wafer off of the supports in the wafer carrier, or there will be interference between the end effector and the wafer carrier supports. Thus, an end effector must be designed to avoid the exclusion zones 100, 102. The end effector 14, shown in FIG. 1a, however. will cross directly into part of the exclusion zones 102.
One solution to avoid the exclusion zones 100, 102 is illustrated by the end effector 12, shown in FIG. 1b. Also. the outline of the end effector 12 is shown, in dashed lines, in FIG. 4 with respect to the exclusion zones. The end effector 12 has a constant width, similar to the end effector 14, except that it tapers almost immediately near the mounting end to a narrower width, which is then constant to the free end. Thus, the two projections at the free end of the end effector 12 will pass between the exclusion zones 102, as illustrated in FIG. 4. A problem with the end effector 12 is that since the supports at the two projections are so close together, the wafer is unstable on these supports. A less stable support structure requires that the wafers be moved more slowly, so they don""t slide on the end effector. Thus, the throughput of the processing system is decreased. Another problem with the supports at the free end of the end effector 12 being so close together is that, since the 300 mm wafer is so large, the wafer may bow, or sag, in the middle. Since the shelves that support the wafer on the end effector 12 may be no more than about 120 mils high, there is the potential for the underside of the wafer to become contaminated by sagging low enough to touch the end effector 12 near its center.
Another solution for avoiding the exclusion zones 100, 102 and providing a stable support and avoiding wafer bowing is to provide an end effector that is wider than end effector 14, so the projections at the free end will pass outside of the exclusion zones 102, but inside the exclusion zones 100. A problem with an end effector that is generally shaped like the end effector 14, but which tapers outward almost immediately to form a constant width, is that its greater mass would cause it to have a greater momentum which would result in slower acceleration and deceleration of the end effector, and consequently, a longer time to move the wafer through the chamber. Another problem with the heavier end effector is that it would require a stronger; and therefore, more expensive; arm assembly 16, 24 to support and move the end effector.
A need, therefore, exists for an end effector that may be used in any chamber with any wafer handler, that avoids the exclusion zones, provides a stable support for the wafers and is light weight.
A vacuum processing system has, in its transfer chamber, buffer chamber and/or mini-environment, environment, a wafer handler with an end effector that, starting at its fixed end, tapers inwardly to side recesses on opposing sides of the end effector and then tapers outwardly to a free end wider than the fixed end and that, at its free end, has another recess defining a pair of fingers with wafer supports thereon. The free end recess extends into the wafer sensor cutout area. The side recesses and the free end recess extend into the end effector to limit the weight of the end effector while maintaining its strength. The side recesses give the end effector a unique hourglass shape.
The pair of fingers providing the wafer supports at the free end of the end effector are spaced wider than the innermost exclusion zones for a standard 300 mm wafer carrier, but closer together than the outermost exclusion zones. In other words, the pair of fingers have inner facing edges that are at least about 150 mm to about 160 mm apart and have outer opposing edges that stable support platform for the wafer and prevents the wafer from bowing.
In one embodiment, the end effector has a three-point support for the wafer at locations near the fixed end of the end effector arid on the two fingers near the free end. The three-point support may be a ball or bump support configuration.